It is now well established that xenon binds to numerous proteins upon moderate pressurization. We recorded significant changes in diffraction intensities from myoglobin crystals, for up to 5 minutes following depressurization from 10 atm of xenon gas. We therefor attempted to trap xenon in the binding site by quickly flash-cooling a myoglobin crystal after depressurization (~5 seconds). The resulting isomorphous difference Patterson map revealed the presence of a well-ordered xenon site indicating that this method may be useful for proteins having xenon off-rates similar or slower than myoglobin.